Low leakage and data retention circuitry

ABSTRACT

An integrated circuit includes first circuitry and sleep transistor circuitry. The first circuitry receives input signals and processes the input signals. The first circuitry also retains data in a sleep state that has low leakage. The sleep transistor circuitry is coupled to the first circuitry and receives a sleep signal that has a negative voltage. The sleep circuitry reduces power consumption of the first circuitry in the sleep state to have low leakage based on the sleep signal while retaining the data in the first circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/546,574 titled “Power Management and Power Savings in IntegratedCircuits,” filed Feb. 19, 2004, which is hereby incorporated byreference. This application also claims the benefit of U.S. ProvisionalApplication Ser. No. 60/586,565 titled “Systems and Methods for I/OPower Island Management and Leakage Control on Integrated Circuits,”filed Jul. 9, 2004, which is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to integrated circuits, and moreparticularly to low leakage and data retention circuitry.

2. Description of the Prior Art

Most integrated circuits have a design goal to reduce the overall powerconsumption. The total power consumed by an integrated circuit includesdynamic power consumption and standby leakage current consumption. Thechallenge in designing an integrated circuit is to reduce the dynamicpower and leakage power, while maintaining performance and cost goalsfor the integrated circuit.

In complementary metal oxide semiconductors (CMOS), various types ofleakage occur such as pn junction reverse-bias current, subthresholdleakage, oxide tunneling current, gate current due to hot-carrierinjection, gate-induced drain leakage, and channel punchthrough current.When the threshold voltage for a CMOS transistor is reduced for higherperformance, the leakage power is significant in the total powerconsumption of the CMOS circuit.

There are two approaches in reducing the leakage power for CMOScircuits. The first approach is a process level technique that controlsthe doping profile of the transistor. The other approach is a circuitlevel technique where voltages at the different device terminals such asthe drain, source, gate, and body are controlled. Some circuit leveltechniques are discussed below.

One circuit level technique is stacking transistors, which is alsocalled self-reverse bias. When more than one transistor in a stack ofseries-connected transistors is turned off, the subthreshold leakagecurrent is reduced. One problem with the transistor stack is that only athree times reduction in leakage current is achieved.

Another circuit level technique is a multiple threshold voltage design.Both high- and low-threshold transistors are on the same chip to dealwith the leakage problem. The high-threshold transistors suppress thesub-threshold leakage current. The low-threshold transistors are used toachieve higher performance. One problem with a multiple threshold designis that process complexity and costs are increased.

Another circuit level technique is a multiple body bias in which thebody voltage is changed to modify the threshold voltage. If separatebody biases are applied to different NMOS transistors, the transistorcannot share the same well, which requires triple well technologies. Oneproblem is that well biasing consumes a lot of chip area and requiresextra power supplies for each cell. This technique also increasesprocess complexity and the leakage reduction is not optimal.

Another technique for reducing leakage is a sleep transistor. FIG. 1depicts prior art circuitry including a sleep transistor. For NMOS sleeptransistors, one or more NMOS transistors are added to logic gates inseries with the cell transistors to VSS. The NMOS sleep transistors actas a switch to turn on and off the logic gate. In FIG. 1, the sleeptransistor 130 is turned on (gate to VDD) during normal cell operation.When the cell is idle, the sleep transistor 130 is turned off (gate tiedto VSS) to reduce the leakage current of the cell. Sleep transistors canalso be PMOS transistors. One problem with sleep transistors is that ifall logic has sleep transistors, the logic will lose their stateinformation.

SUMMARY OF THE INVENTION

The invention addresses the above problems by providing systems andmethods for low leakage, data retention circuitry. An integrated circuitincludes first circuitry and sleep transistor circuitry. The firstcircuitry receives input signals and processes the input signals. Thefirst circuitry also retains data in a sleep state that has low leakage.The sleep transistor circuitry is coupled to the first circuitry andreceives a sleep signal that has a negative voltage. The sleep circuitryreduces power consumption of the first circuitry in the sleep state tohave low leakage based on the sleep signal while retaining the data inthe first circuitry.

In some embodiments, the sleep signal indicates a power up state and thesleep transistor powers up the first circuitry based on the sleepsignal. In some embodiments, the first circuitry receives a hold signaland retains the data based on the hold signal. In some embodiments, thefirst circuitry includes master latch circuitry and slave latchcircuitry that retains the data in the powered down state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of circuitry including a sleep transistor inthe prior art;

FIG. 2 is an illustration of an integrated circuit with a power supplyin an exemplary implementation of the invention;

FIG. 3 is an illustration of a power island manager with an isolationgate and a D flip-flop in an exemplary implementation of the invention;

FIG. 4 is an illustration of a power island manager in an exemplaryimplementation of the invention;

FIG. 5 is an illustration of a D/Q portion of flip-flop circuitry in anexemplary implementation of the invention;

FIG. 6 is an illustration of a CK portion of flip-flop circuitry in anexemplary implementation of the invention;

FIG. 7A is an illustration of a sleep transistor for an OFF node in anexemplary implementation of the invention;

FIG. 7B is an illustration of a sleep transistor for an SB node in anexemplary implementation of the invention;

FIG. 7C is an illustration of a moderate impedance transistor for an SBnode in an exemplary implementation of the invention;

FIG. 8A is an illustration of circuitry for a tristate inverter in themaster latch in an exemplary implementation of the invention;

FIG. 8B is an illustration of circuitry for a tristate inverter in theslave latch in an exemplary implementation of the invention;

FIG. 9 is an illustration of a HOLDB and SLEEPB signals in an exemplaryimplementation of the invention;

FIG. 10 is an illustration of circuitry for low leakage and dataretention in an exemplary implementation of the invention;

FIG. 11 is an illustration of slave latch circuitry in an exemplaryimplementation of the invention; and

FIG. 12 is an illustration of circuitry for a level shifter for an I/Opad in an exemplary implementation of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in the exemplary drawings wherein like reference numeralsindicate like or corresponding elements among the figures, exemplaryembodiments of a system and method according to the present inventionare described below in detail. It is to be understood, however, that thepresent invention may be embodied in various forms. Therefore, specificdetails disclosed herein are not to be interpreted as limiting, butrather as a basis for the claims and as a representative basis forteaching one skilled in the art to employ the present invention invirtually any appropriately detailed system, structure, method, processor manner.

Power Island Manager—FIGS. 2-4

In some embodiments, an integrated circuit can be delineated into powerislands. Power consumption can then be controlled within the powerisland. A power island manager provides control signals to the powerisland to control power consumption of the power island. In someembodiments, the low leakage, data retention circuitry is located withinthe power islands.

FIG. 2 depicts an illustration of an integrated circuit 200 with a powersupply 280 in an exemplary implementation of the invention. Theintegrated circuit 200 includes a central processing unit (CPU) 210, aclock manager 212, power island managers 220, 222, and 224, a powersupply manager 240, level shifter/isolation gates (LS/ISO) 250, 252, and254, logic (power island 2) 260, memory (power island 0) 262, thirdparty intellectual property (IP) (power island 1) 264, adaptive leakagecontroller (ALC) 270, and bus 280.

A power island is any section, delineation, partition, or division of anintegrated circuit where power consumption is controlled within thesection, delineation, partition, or division. In some embodiments, thepower islands are delineated based on geographic factors of theintegrated circuit. In some embodiments, the power islands aredelineated based on functional IP units of the integrated circuit 200.In this example depicted in FIG. 2, power islands are delineated bymemory 262, logic 260, and third party IP 264. Power islands arediscussed in further detail in pending U.S. application Ser. No.10/840,893 entitled “Managing Power on Integrated Circuits Using PowerIslands” filed on May 7, 2004, which is hereby incorporated byreference.

The power island managers 220, 222, and 224 are any circuitry, device,or system configured to provide control signals to a power island tocontrol power within the power island. The power island managers 220,222, and 224 can dynamically change the power consumption of the powerislands based on the needs and operation of the integrated circuit 200.The power island managers 220, 222, 224 may select a clock, change clockfrequency, or modify the voltage within the power island to control thepower consumption of the power island.

The ALC 270 provides control signals to compensate for process andtemperature variation to provide the optimum voltage to be applied tosleep transistors in the power islands. The ALC 270 is described infurther detail U.S. patent application Ser. No. 10/996,739 entitled“Systems and Methods for Minimizing Static Leakage of an IntegratedCircuit” filed on Nov. 17, 2004.

FIG. 3 depicts an illustration of the power island manager 220 with anisolation gate 350 and a D flip-flop 360 in an exemplary embodiment ofthe invention. The power island manager 220 includes a data retentionstate machine 330 and a sleep generator 340 that are coupled to eachother.

The power island manager 220 is coupled to the isolation gate 350 by theISO signal. The ISO signal is also coupled to other isolation gates. Thedata retention state machine 330 is coupled to DRB input of the Dflip-flop 360 via the DRB signal. The data retention state machine 330is also coupled to the AND gate 362 via the ENC signal. The clock island(CKI) signal is coupled to the data retention state machine 330 and theAND gate 362. The sleep generator 340 is coupled to the D flip-flop 360and the AND gate 362 via the SLPB signal. The output of the AND gate 362is coupled to the C input of the D flip-flop 360 via the CKA signal. Thesystem reset signal is coupled to the RESETB input of the power islandmanager 220 and the RB input of the D flip-flop 360. The SLPB signal,the DRB signal, and the system reset signal are coupled to other dataretention flip-flops.

FIG. 4 depicts an illustration of a power island manager 220 in anexemplary embodiment of the invention. The power island manager 220includes an AND gate 402, a multiplexer (MUX) 404, a D flip-flop 410, aninverter 412, an AND gate 414, a D flip-flop 420, a D flip-flop 430, thedata retention state machine 330, a MUX 432, a MUX 442, a sleepgenerator 340, and a buffer 452.

The DI0 pin is coupled to the D input of the D flip-flop 410. The SI0pin is coupled to the SI input of the D flip-flop 410. The CSB and theWEB pins are coupled to the inputs of the AND gate 402. The output ofthe AND gate 402 and the SCK1 pin are coupled to the input of the MUX404. The output of the MUX 404 is coupled to the C inputs of the Dflip-flop 410, the D flip-flop 420, and the D flip-flop 430. The Qoutput of the D flip-flop 410 is coupled to the DO0 pin, which iscoupled to the input of the inverter 412 and the SI input of the Dflip-flop 420. The DI1 pin is coupled to the D input of the D flip-flop420. The Q output of the D flip-flop 420 is coupled to the DO1 pin,which is coupled to the input of the AND gate 414 and the SI input ofthe D flip-flop 430. The output of the AND gate 414 is coupled to theRSTB pin. The DI2 pin is coupled to the D input of the D flip-flop 430.The Q output of the D flip-flop 430 is coupled to the DO2 pin, which iscoupled to the DLY1/ISO pin. The DLY1/ISO pin is coupled to the SO1, theinput of the MUX 432, and the data retention state machine 340.

The RESETB pin is coupled to the R input of the D flip-flop 430, the Dflip-flop 420, and the D flip-flop 410. The SE pin, the RESETB pin, theCKI pin, and the SI2 pin are coupled to the data retention state machine330. The data retention state machine 330 is coupled to the input of theMUX 432, the SO2 pin, the DRB pin, the ENC pin, and the input of the MUX442. The output of the MUX 442, the VDDI pin, and the VL[0:2] arecoupled to the sleep generator 340. The sleep generator 340 is coupledto the SLPB pin. The sleep generator 340 is coupled to the dataretention state machine 330 via the AW pin and the input of the buffer452. The output of the buffer 452 is coupled to the DO3 pin. The DRMODEpin is coupled to the MUX 442.

In operation, the power island manager 220 has a three bit register forcontrolling a power island for some embodiments. D [0], with input DI0and output DO0, is an island reset for re-initializing a power island.This bit is combined with RESETB to form RSTB to re-initialize the powerisland whenever RESETB or the D [0] is active. D [1], with input DI1 andoutput DO1, is a sleep bit. When the D [1] bit is set to one, the powerisland goes into a low leakage state. D [2], with input DI2 and outputDO2, is a DLY1/Isolate bit. When DRMODE is tied to low, the D [2] bit,when set to one, will add one clock cycle delay between DRB going activeand SLPB going active. When DRMODE is tied high, the D [2] bit, when setto one, will activate isolation of the power island. D [3], such as DO3,is an awake bit. This D [3] bit goes high when SLPB is high. This can beused by software to determine when a power island is out of the sleepstate.

The power island manager 220 has two operating modes: one that supportspower islands with data retention flip-flops and one that does not. Whenthe DRMODE pin is tied high, a power island is put to sleep by writing aone to D[1]. The data retention state machine 330 performs the timing.The isolate (ISO) signal goes active when the sleep bit is written to aone, and the enable clock (ENC) and the data retention (DRB) will go lowafter synchronization to the power island clock (CKI). One or two clockcycles later the sleep (SLPB) goes low. To come out of sleep mode, azero is written to D[1]. In some embodiments, all clock buffers in thepower islands can be put to sleep to further minimize leakage. Softwarecan determine when the power island has come out of sleep by readingwhen DO3 is high.

The System Reset is typically applied once after initial system powerup. In some embodiments, the System Reset goes to all data retentionflip-flops. The System Reset signal and DI0 bar are combined in alogical AND (RSTB output) to provide initialization to non dataretention flip-flops. To create a power island reset, D[0] is set to aone and then cleared to a zero by software.

When the DRMODE is tied low, the power island manager 220 can alsoprovide the control signals for a power island without data retentionflip-flops. The power island manager 220 may have a hardware drivenmethod and a software driven method for interfacing to power islandswithout data retention flip-flops. The software sequence has thefollowing sequence:

-   -   Write 04 /turn on isolation    -   Write 06 /turn on sleep, isolation on /come out of sleep    -   Write 05 /turn sleep off, reset island, isolation on /wait for        sleep to go high    -   Read /test for DO3=1; sleep is high    -   Write 00 /turn isolation off, normal operation

The hardware driven method uses a clock to sequence the state machine.The only action software takes is to write the sleep bit (DI1) to a oneto go into sleep and write a zero to the sleep bit to go out of sleep.Software can determine when the island has come out of sleep by readingwhen DO3 is high.

In some embodiments, the power island manager 220 contains two scanchains because some of the flip-flops are clocked on the positive andsome on the negative. The scan chain enable pin switches the clock onscan chain 1 (SI1 is the input; SO1 is the output), the registers, toCKS1. Scan chain 2 (SI2 is the input; SO2 is the output) is connected tothe data retention state machine 330 flip-flops that are clocked on thenegative edge of CKI. A separate scan out is provided for each clockdomain.

In some embodiments, the SLPB net uses p-type antenna diodes. Since theSLPB net may go to a negative voltage, an n-type antenna diode can causeexcessive leakage to ground. The leakage can cause SLPB not to gonegative and may not work properly. The CSB pin is a chip select pin.The WEB pin is the write enable pin. The VL [2:0] is the leakage controlvoltage value set by the ALC 270 (FIG. 2). The VDDI is the VDD from thepower island.

Low Leakage, Data Retention Circuitry—FIGS. 5, 6, 7A-C, 8A-8B, and 9-12

FIGS. 5, 6, 7A-C, and 8A-8B disclose one embodiment for low leakage,data retention circuitry. In this embodiment, in sleep mode, the circuitparts of a flip-flop that do not require data retention are coupled toground through a sleep transistor. The gate of the sleep transistor iscoupled to a sleep signal that can be driven to a negative voltage suchas −0.3V. Thus, the leakage in these circuit parts of the flip-flop iseliminated (reduced). When not in a sleep state, the sleep transistorhas a gate value equal to or greater than the VDD supply, whicheffectively grounds the circuit.

The circuit parts that require data retention are coupled to groundthrough two transistors. One transistor acts effectively to ground thecircuit above when not in sleep mode just as the sleep transistordescribed above. The other transistor is a PMOS device with the gatetied to ground, which provides medium impedance to ground. The voltagedrop across this transistor acts to reduce the leakage by increasing thesource bias of the NMOS transistors and simultaneously reduces thevoltage across the circuit. In this embodiment, the data is retained ina sleep state and reduces the leakage by a factor of 22.

FIG. 5 depicts an illustration of a D/Q portion 500 of the flip-flopcircuitry in an exemplary implementation of the invention. The D/Qportion 500 of the flip-flop circuitry includes an inverter 502, a M3PMOS transistor 504, an M4 NMOS transistor 506, master latch circuitry510, an M11 PMOS transistor 522, an M12 NMOS transistor 524, an M13 NMOStransistor 526, slave latch circuitry 530, and an inverter 540.

The D signal input is the input of the inverter 502, which includestransistors M1 and M2. The source of the inverter 502 is coupled to thenode OFF, which is described below in FIG. 7A. The output of theinverter 502 is coupled to the M3 PMOS transistor 504 and the M4 NMOStransistor 506. The gate of the M3 PMOS transistor 504 is coupled to theCLK signal input. The gate of the M4 NMOS transistor 506 is coupled tothe CLKB signal input.

The master latch circuitry 510 includes the inverter 512 and theinverter 514. The inverter 514 forms a feedback loop with the inverter512, where the output of the inverter 512 is coupled to the input of theinverter 514 and the output of the inverter 514 is coupled to the inputof the inverter 512. The inverter 512 corresponds to transistor M5 andM6. The inverter 514 corresponds to transistors M7-M10. The input of theinverter 512 is coupled to node A, which is described in FIG. 8A below.The source of the inverter 512 is also coupled to node OFF, which isdescribed below in FIG. 7A. The output of the inverter 512 is coupled tonode B, which is described below in FIG. 8A. The source of the inverter514 is coupled to node OFF, which is described below in FIG. 7A. ThePMOS gate of the inverter 514 is coupled to the CLKB signal input. TheNMOS gate of the inverter 514 is coupled to the CLK signal input.

The M11 PMOS transistor 522 is in parallel to the M12 NMOS transistor524 and the M13 NMOS transistor 526, which are in series. The gate ofthe M11 PMOS transistor 522 is coupled to the CLKB signal input. Thegate of the M12 NMOS transistor 524 is coupled to the HOLDB signalinput. The gate of the M13 NMOS transistor 526 is coupled to the CLKsignal input.

The slave latch circuitry 530 includes the inverter 532 and the inverter534. The inverter 534 forms a feedback loop with the inverter 532, wherethe output of the inverter 532 is coupled to the input of the inverter534 and the output of the inverter 534 is coupled to the input of theinverter 532. The inverter 532 corresponds to transistor M14 and M15.The inverter 534 corresponds to transistors M18-21 and M31. The input ofthe inverter 532 is coupled to node C, which is described in FIG. 8Bbelow. The source of the inverter 532 is also coupled to node SB, whichis described below in FIGS. 7B-C. The output of the inverter 532 iscoupled to node D, which is described below in FIG. 8B. The source ofthe inverter 534 is coupled to node SB, which is described below inFIGS. 7B-C. The PMOS gates of the inverter 534 are coupled to the HOLDBand CLK signal inputs. The NMOS gate of the inverter 534 is coupled tothe CLKB signal input.

The output of the inverter 532 is coupled to the input of the inverter540. The inverter 540 corresponds to transistors M16 and M17. The sourceof the inverter 540 is also coupled to node OFF, which is describedbelow in FIG. 7A. The output of the inverter 540 is the Q signal output.

FIG. 6 depicts a CK portion 600 of the flip-flop circuitry in anexemplary implementation of the invention. The CK portion 600 of theflip-flop circuitry includes an inverter 602, an M24 PMOS transistor604, an M25 PMOS transistor 606, an M26 NMOS transistor 608, an M32 NMOStransistor 610, and an M27 PMOS transistor 612.

The CK signal input is the input of the inverter 602, which includestransistors M22 and M23. The source of the inverter 602 is coupled tonode OFF, which is described below in FIG. 7A. The output of theinverter 602 is coupled to the drain of the M24 PMOS transistor 604 andthe node CLKB. The gate of the M24 PMOS transistor 604 is coupled to theHOLDB signal input. The output of the inverter 602 is also coupled tothe M25 PMOS transistor 606 and the M26 NMOS transistor 608. The M25PMOS transistor 606, the M26 NMOS transistor 608, and the M32 NMOStransistor 610 are coupled in series. The gate of the M32 NMOStransistor 610 is coupled to the HOLDB signal input.

The CLK signal output is coupled to the drain of the M25 PMOS transistor606, the drain of the M26 NMOS transistor 608, and the drain of the M27PMOS transistor 612. The gate of the M27 PMOS transistor 612 is coupledto the HOLDB signal input.

FIG. 7A depicts a sleep transistor 702 for the OFF node in an exemplaryimplementation of the invention. The sleep transistor 702 is an NMOStransistor that corresponds to transistor M28. The drain of the sleeptransistor 702 is coupled to the OFF node. The gate of the sleeptransistor 702 is coupled to the SLEEPB signal input. The source of thesleep transistor 702 is coupled to ground. In some embodiments, the OFFnode can be separated into two or more nodes each having its own NMOSsleep transistor.

FIG. 7B depicts a sleep transistor 704 for the SB node in an exemplaryimplementation of the invention. The sleep transistor 704 is an NMOStransistor that corresponds to transistor M29. The drain of the sleeptransistor 704 is coupled to the SB node. The gate of the sleeptransistor 704 is coupled to the SLEEPB signal input. The source of thesleep transistor 704 is coupled to ground.

FIG. 7C depicts a sleep transistor 706 for the SB node in an exemplaryimplementation of the invention. The sleep transistor 706 is a PMOStransistor that corresponds to transistor M30. The source of the sleeptransistor 706 is coupled to the SB node. The gate and drain of thesleep transistor 706 are coupled to ground.

FIG. 8A depicts circuitry 800 for the tristate inverter in the masterlatch in an exemplary implementation of the invention. The circuitry 800for the master latch includes a PMOS transistor 802, a PMOS transistor804, an NMOS transistor 806, and an NMOS transistor 808 that are coupledtogether in series. The gates of the PMOS transistor 802 and the NMOStransistor 808 are coupled to the node B. The gate of the PMOStransistor 804 is coupled to the CLKB signal input. The gate of the NMOStransistor 806 is coupled to the CLK signal input. The drains of thePMOS transistor 804 and the NMOS transistor 806 are coupled to node A.The source of the NMOS transistor 808 is coupled to node OFF.

FIG. 8B depicts circuitry 810 for the tristate inverter in the slavelatch in an exemplary implementation of the invention. The circuitry 810for the slave latch includes a PMOS transistor 812, a PMOS transistor814, a PMOS transistor 816, an NMOS transistor 818, and an NMOStransistor 820. The PMOS transistor 812 is coupled to the PMOStransistor 814 and the PMOS transistor 816 that are parallel to eachother. The PMOS transistor 814 and the PMOS transistor 816 are coupledto the NMOS transistor 818, which is also coupled to the NMOS transistor820.

The gates of the PMOS transistor 812 and the NMOS transistor 820 arecoupled to the node D. The gate of the PMOS transistor 814 is coupled tothe HOLDB signal input. The gate of the PMOS transistor 816 is coupledto the CLK signal input. The gate of the NMOS transistor 818 is coupledto the CLKB signal input. The drains of the PMOS transistor 814, thePMOS transistor 816, and the NMOS transistor 806 are coupled to node C.The source of the NMOS transistor 820 is coupled to node SB.

FIG. 9 depicts an illustration of the HOLDB and SLEEPB signals in anexemplary embodiment of the invention.

The operation begins with CK going to zero. This causes CLKB to be equalto VDD and CLK to be equal to zero, which isolates the slave latchcircuitry 530 from the master latch circuitry 510. The HOLDB signal goesto 0 to retain the state of the slave latch. The SLEEPB signal then goesto −0.3V. This shuts off transistor M28 in FIG. 7A, which halts theleakage from all the circuits except in the slave latch circuitry 530.When not in sleep mode, transistor M28 provides a low impedance path toground.

The slave latch circuitry 530 is coupled to ground through thetransistors M29 and M30, respectively depicted in FIGS. 7B and 7C. Onepurpose of transistor M29 is to provide a low impedance path to groundwhen not in sleep mode.

One purpose of transistor M30 is to provide a default moderate impedancepath to ground when transistor M29 is off or in sleep mode. The leakagein the slave latch circuitry 530, in going through transistor M30,causes node SB to rise. This provides a source bias to the slave NMOStransistors reducing the leakage through them and also reduces thevoltage across the slave side to VDD−SB, which further reduces theleakage. Equilibrium is reached where the leakage cannot increase.Basically, the leakage is used to limit itself.

This embodiment uses the gated VDD solution because the voltage acrossthe circuit is reduced to VDD−SB. This embodiment combines this gatedVDD with the modulated back gate bias method because of the source biasSB but only for the NMOS transistors. This is accomplished withoutswitching a lower VDD and driving a well. Thus, a simple process can beused. Also, this embodiment advantageously uses the moderate impedancetransistor in a way that causes leakage to limit itself by reachingequilibrium.

FIGS. 10 and 11 disclose another embodiment for low leakage, dataretention circuitry. In this embodiment, in a sleep state, thecircuitries that do not require data retention are coupled to groundthrough a sleep transistor. The logic coupled to the transistors gatedby the SLEEPB signal is shut off and draws minimal leakage. This processis accomplished by driving the SLEEPB signal below VSS by 0.3-0.4V. TheHOLDB signal keeps the slave latch circuitry from changing state whilethe rest of the flip-flop comes out of the sleep state. The only part ofthe flip-flop still powered is the slave latch circuitry. The slavelatch circuitry combines several techniques to minimize leakage.

FIG. 10 depicts circuitry 1000 for low leakage and data retention in anexemplary embodiment of the invention. The circuitry 1000 includes theinverter 1002, the master latch circuitry 1010, the slave latchcircuitry 1020, the inverter 1032, the inverter 1034, the sleeptransistors 1042, 1044, 1046, and 1048, the inverter 1052, and theinverter 1054.

The D input is the input for the inverter 1002. The master latchcircuitry 1010 includes the transmission gate 1012, the inverter 1014,the transmission gate 1016, and the inverter 1018. The output of theinverter 1002 is coupled to the left contact of the transmission gate1012. The right contact of the transmission gate 1012 is coupled to theinput of the inverter 1014 and the left contact of the transmission gate1016. The output of the inverter 1014 is coupled to the D input of theslave latch circuitry 1020 and the input of the inverter 1018. Theoutput of the inverter 1018 is coupled to the DB input of the slavelatch circuitry 1020 and the right contact of the transmission gate1016.

The SLEEPB signal input is coupled to the gates for the SL1 sleeptransistor 1042, the SL2 sleep transistor 1044, the SL3 sleep transistor1046, the SL4 sleep transistor 1048, and the SLEEPB input of the slavelatch circuitry 1020. The SL1 sleep transistor 1042 is coupled to theinverter 1002 and ground. The SL2 sleep transistor 1044 is coupled tothe inverter 1052, the inverter 1054, and ground. The SL3 sleeptransistor 1046 is coupled to the inverter 1014, the inverter 1018, andground. The SL4 sleep transistor 1048 is coupled to the inverter 1032,the inverter 1034, and ground. In some embodiments, the SL1 sleeptransistor 1042, the SL2 sleep transistor 1044, the SL3 sleep transistor1046, and the SL4 sleep transistor 1048 can each be separated into twoor more node each having its own NMOS sleep transistor.

The CK signal is the input of the inverter 1052. The output of theinverter 1052 is coupled to the transmission gate 1012, the transmissiongate 1016, and the input of the inverter 1054. The output of theinverter 1054 is coupled to the transmission gate 1012, the transmissiongate 1016, and the CLK input of the slave latch circuitry 1020. TheHOLDB signal input is coupled to the HOLDB input of the slave latchcircuitry 1020. The output of the slave latch circuitry 1020 is coupledto the input of the inverter 1032. The output of the inverter 1032 iscoupled to the input of the inverter 1034. The output of the inverter1034 is the Q signal.

FIG. 11 depicts slave latch circuitry 1020 in an exemplary embodiment ofthe invention. The slave latch circuitry 1020 includes D1 transistor1102, D2 transistor 1104, DH transistor 1106, DSL sleep transistor 1108,stack transistors 1110, stack transistors 1120, D1B transistor 1132, D2Btransistor 1134, DHB transistor 1136, and sleep transistor 1138.

The D1 transistor 1102, the D2 transistor 1104, the DH transistor 1106,and the DSL sleep transistor 1108 are coupled to each other in serieswith the sleep transistor 1108 coupled to ground. The gate of the D1transistor 1102 is coupled to the CLK signal input. The gate of the D2transistor 1104 is coupled to the D signal input. The gate of the DHtransistor 1106 is coupled to the HOLDB signal input. The gate of thesleep transistor 1108 is coupled to the SLEEPB signal input.

The stack transistors 1110 comprise P1 transistor 1112, P0 transistor1114, N1 transistor 1116, and N0 transistor 1118. The P1 transistor1112, the P0 transistor 1114, the N1 transistor 1116, and the N0transistor 1118 are coupled to each other in series with the N0transistor 1118 coupled to ground. The gates of the P1 transistor 1112,the P0 transistor 1114, the N1 transistor 1116, and the N0 transistor1118 are coupled to the LAT signal input. The drains of the P0Btransistor 1124 and the NIB transistor 1126 are coupled to the LATsignal input.

The stack transistors 1120 comprise P1B transistor 1122, P0B transistor1124, N1B transistor 1126, and N0B transistor 1128. The P1B transistor1122, the P0B transistor 1124, the N1B transistor 1126, and the N0Btransistor 1128 are coupled to each other in series with the N0Btransistor 1128 coupled to ground. The gates of the P1B transistor 1122,the P0B transistor 1124, the N1B transistor 1126, and the N0B transistor1128 are coupled to the LATB signal input. The drains of the P0transistor 1114 and the N1 transistor 1116 are coupled to the LATBsignal input.

In operation, the logic coupled to the transistors gated by the SLEEPBsignal is shut off and draws minimal leakage. This process isaccomplished by driving the SLEEPB signal below VSS by 0.3-0.4V. TheHOLDB signal keeps the slave latch circuitry 1020 from changing statewhile the rest of the flip-flop comes out of the sleep state. The onlypart of the flip-flop still powered is the slave latch circuitry 1020.The slave latch circuitry 1020 combines several techniques to minimizeleakage. Transistors not necessary for state retention (stacks with CLK)have sleep transistors to shut off leakage (gated by the SLEEPB signal).

The 8 transistors in the stack transistors 1110 and 1120 use twotechniques to reduce leakage. The first technique used is transistorstacking, which is also called self-reverse bias. The N0 transistor 1118and the N1 transistor 1116 will have some small leakage even when thegate is at 0V. As a result, VNN1 will be at a positive voltage. Thiscauses VGS(N1) and VBS(N1) to be negative, and VDS(N1) to decrease.Consequently, the leakage current is reduced in N0 transistor 1118 andthe N1 transistor 1116. The same effect occurs on N0B transistor 1128,NIB transistor 1126, P0 transistor 1114, P1 transistor 1112, P0Btransistor 1124, and P1B transistor 1122.

The second technique is called multiple threshold transistors.Increasing channel length of MOS transistors increases the threshold ofthe devices without any change in process complexity. The N0 transistor1118, the N1 transistor 1116, the N0B transistor 1128, and the NIBtransistor 1126 have increased channel length, which raises VTH andreduces leakage current.

This embodiment reduces leakage by a factor of 25 over a currentstandard cell D flip-flop.

I/O Pad—FIG. 12

In some embodiments, a programmable general purpose input and output(I/O) padcell includes built in-level shifters and isolation thatinterface with the chip core logic. In these embodiments, a levelshifter can be controlled to retain data.

FIG. 12 depicts circuitry 1200 for a level shifter for an I/O pad in anexemplary embodiment of the invention. The circuitry 1200 includes MP2transistor 1202, MP3 transistor 1204, M3 transistor 1206, M4 transistor1208, M1 transistor 1210, M0 transistor 1212, M5 transistor 1214, M2transistor 1216, and an inverter 1218.

The circuitry 1200 is for a latching level shifter. The M3 transistor1206 and the M4 transistor 1208 are “native” cascode devices. The M3transistor 1206 and the M4 transistor 1208 are also known asdepletion-mode transistors. The M3 transistor 1206 and the M4 transistor1208 are used to allow thin gate devices to be used in the input stage.This allows large voltage ratios between the VDD and the V3IO. The M0transistor 1212 and the M1 transistor 1210 are output latching devicesthat allow the level shifter to retain the state when both IN and INBare 0. Thus, IN and INB control data retention.

In some embodiments, the gates of the M3 transistor 1206 and the M4transistor 1208 are coupled to other transistors connected to thecascode voltage.

The following truth table is for circuitry 1200. IN INB OUT 0 0 Retainlast state 0 1 0 1 0 1 1 1 Illegal

There will be setup time requirements for any signal compared to SLPB.If level shifters are used with an SRAM cell built into the outputstage, the two inputs can be removed anytime after the output latch hasflipped to a new state. Both 1.2V inputs to the level shifter cannot goto VDD. This can be prevented by including an inverter. If both theinverter and the level shifter have SLPB transistors, there is apotential timing race if SLPB goes to VSS with VDD high. In this case,the level shifters should be off before the output of the inverterdrifts to VDD. In some embodiments, the M5 transistor 1214 and the M2transistor 1216 can be configured to withstand greater voltages.

In some embodiments, the sources of the M5 transistor 1214 and the M2transistor 1216 can be coupled to a common SLEEPB transistor to furtherreduce leakage. In one embodiment, the width of the SLEEPB transistor is4 micrometers, and the length is 0.13 micrometers. The following truthtable is for circuitry 1200 including this common SLEEPB transistor:SLEEPB IN INB OUT 1 0 0 Retain state (Data Retention) 1 0 1 0 1 1 0 1 11 1 Illegal 0 X X Retain State

In some embodiments, the SLEEPB=0 input state should be understood toinclude the SLEEPB voltage being below 0V (E.g. −0.35V generated by aleakage optimization circuit).

In this extension to FIG. 12 (and the above truth table), the two DataRetention states may be operated independently, sequentially orsimultaneously. This is beneficial when the SLEEPB input is used tocontrol/limit leakage power while the IN/INB=00 state is used for dataretention. This is because the SLEEPB voltage comes from a charge pumpand takes some time to transition from Vdd (=1) to the Data Retentionmode.

The above description is illustrative and not restrictive. Manyvariations of the invention will become apparent to those of skill inthe art upon review of this disclosure. The scope of the inventionshould, therefore, be determined not with reference to the abovedescription, but instead should be determined with reference to theappended claims along with their full scope of equivalents.

1. An integrated circuit comprising: first circuitry configured to receive input signals, process the input signals, and retain data in a sleep state that has low leakage; sleep transistor circuitry coupled to the first circuitry and configured to receive a sleep signal that has a negative voltage and reduce power consumption of the first circuitry in the state to have low leakage based on the sleep signal while retaining the data in the first circuitry.
 2. The integrated circuit of claim 1 wherein the sleep signal indicates a power up state and the sleep transistor circuitry is configured to power up the first circuitry based on the sleep signal.
 3. The integrated circuit of claim 1 wherein the first circuitry is configured to receive a hold signal and retain the data based on the hold signal.
 4. The integrated circuit of claim 1 wherein the first circuitry comprises master latch circuitry and slave latch circuitry and wherein the slave latch circuitry is configured to retain the data in the sleep state.
 5. The integrated circuit of claim 4 wherein the slave latch circuitry comprises a medium impedance transistors configured to bias sources in the slave latch circuitry.
 6. The integrated circuit of claim 4 wherein the slave latch circuitry comprises stacked transistors configured to minimize leakage.
 7. The integrated circuit of claim 4 wherein the slave latch circuitry comprises multiple threshold transistors configured to minimize leakage.
 8. The integrated circuit of claim 1 further comprising a power island manager configured to generate and transmit the sleep signal.
 9. The integrated circuit of claim 1 wherein the first circuitry is located within a power island.
 10. The integrated circuit of claim 1 further comprising an adaptive leakage controller configured to determine the negative voltage of the sleep signal.
 11. The integrated circuit of claim 1 wherein the first circuitry is configured to receive a control signal to deactivate the sleep state.
 12. The integrated circuit of claim 1 wherein the sleep transistor comprises an NMOS transistor.
 13. A method for operating an integrated circuit, the method comprising: receiving input signals into first circuitry; processing the input signals in the first circuitry; retaining data in a sleep state that has low leakage in the first circuitry; receiving a sleep signal that has a negative voltage into sleep transistor circuitry coupled to the first circuitry; and in the sleep transistor circuitry, reducing power consumption of the first circuitry in the sleep state to have low leakage based on the sleep signal while retaining the data in the first circuitry.
 14. The method of claim 13 wherein the sleep signal indicates a power up state and the method further comprising in the sleep transistor circuitry, powering up the first circuitry based on the sleep signal.
 15. The method of claim 13 further comprising: receiving a hold signal into the first circuitry; and retaining the data based on the hold signal.
 16. The method of claim 13 wherein the first circuitry comprises master latch circuitry and slave latch circuitry and the method further comprising in the slave latch circuitry, retaining the data in the sleep state.
 17. The method of claim 16 further comprising minimizing leakage using a medium impedance transistor to bias sources in the slave latch circuitry.
 18. The method of claim 16 further comprising minimizing leakage using stacked transistors in the slave latch circuitry.
 19. The method of claim 16 further comprising minimizing leakage using multiple threshold transistors in the slave latch circuitry.
 20. The method of claim 13 further comprising generating and transmitting the sleep signal from a power island manager.
 21. The method of claim 13 wherein the first circuitry is located within a power island.
 22. The method of claim 13 further comprising determining the negative voltage of the sleep signal in an adaptive leakage controller.
 23. The method of claim 13 further comprising receiving a control signal to deactivate the sleep state in the first circuitry.
 24. The method of claim 13 wherein the sleep transistor comprises an NMOS transistor.
 25. A latching level shifter circuitry comprising: level shifter circuitry with inputs and outputs; and output latching circuitry comprising at least two transistors coupled to the outputs of the level shifter circuitry and configured to retain a state of the level shifter circuitry based on the inputs. 